The subject matter disclosed herein relates to coated belts or ropes used, for example, in elevator systems. More specifically, the subject disclosure relates to wear detection (e.g. detection of corrosion, fretting, etc.) of coated belts or ropes used for elevator suspension and/or driving.
Elevator systems utilize ropes or belts operably connected to an elevator car, and routed over one or more sheaves, also known as pulleys, to propel the elevator car along a hoistway. Coated steel belts in particular include a plurality of wires located at least partially within a jacket material. The plurality of wires is often arranged into one or more strands and the strands are then arranged into one or more cords. In an exemplary belt construction, a plurality of cords is typically arranged equally spaced within a jacket in a longitudinal direction.
During normal elevator operation, coated steel belts are subjected to a large number of bending cycles as the belt travels over drive sheaves and deflector sheaves of the elevator system. These bending cycles cause a degradation of the breaking strength of the wires or cords within the coated steel belt via the mechanism of wire fretting or fatigue. Such fatigue is a major contributor to reduction in service life of the coated steel belt. While the service life of the coated steel belt can be estimated through calculation, a more accurate estimation of remaining life of the coated steel belt is often obtained by utilizing a life-monitoring system.
One such system is called resistance-based inspection (RBI). An RBI system is secured to the coated belt or rope at a fixed point of the elevator system and monitors a change in electrical resistance of one or more of the cords in the belt or rope. Since the electrical resistance of each cord is proportional to its cross-sectional area, changes is electrical resistance can be correlated to reduction in cross-sectional area of the cord, indicating an amount of fretting of the cord, and a corresponding remaining service life. The changes in electrical resistance are determined relative to a baseline resistance, typically taken at installation of the system. This initial reading compensates for cord temperature by measuring temperature at the monitoring unit, and then assumes the relationship between cord and monitoring unit temperature to be fixed over the life of the cord. Cord temperature has a significant effect on cord resistance, and therefore inaccuracy in cord temperature could lead to false alarms or false indications of adequate remaining cord life.